866
Appendix IL
The advantage of the alteration is self-evident, being largely
due to the fact that with electric driving the principal losses
vary with the load, and are not constant as with shafting.
P. 504. Velocity-ratio in Hooke's Joint.—Given a
universal or Hooke's joint, its construction is essentially that of
two forks pivoted to a cross, as in Fig. 829. Now let circle
PTQ shew plane of motion of P and Q, while PRQ (an ellipse
in elevation, but really a circle) indicates that of s and R. Let
p move to P! while R moves to Ra; then angles P o Pa and R o Ra
are equal, the latter being that apparent in elevation and not
the real one on plane s R. Draw Ra R2 || R T, and join o R2.
TOR2 is the real angular motion of R, while that of P is POPr
Calling p's velocity v, and R'S velocity ^:
£>! TR2 RRj Or
When P arrives at T, and R at Q, the velocity relations are
exactly reversed, for the fork positions have simply interchanged.
Join R Q and draw T w || R Q, thus making o R : O T : : o Q : o w ;
and complete the quarter ellipse R w. Then the, radii vector o P